Fiber characterization can be defined as the field measurement and recording of fiber span parameters that affect signal transmission over all or selected operating wavelengths. These measured parameters provide a true picture of the fiber span’s transmission limitations. They are used in network planning to ensure transmission links are designed within transceiver operating budgets and limits. Full fiber characterization is often necessary in modern high-speed link designs, where optical budgets are stretched to their maximum with little or no margin for error. Fiber quality can also be assessed with these parameters. Fiber characterization is performed after new fiber cable link construction, dark fiber purchase, or lease. This helps to ensure the fiber quality meets or exceeds required specifications and expectations. It also documents fiber parameters at the time of construction or acquisition for comparison with future measurements to determine fiber degradation due to aging, damage, and repair.